The following description is provided simply as an aid in understanding the disclosure and is not admitted to describe or constitute prior art.
The present invention relates generally to optimally operating electric power grids, and more particularly, to methods and systems for operating solid oxide fuel cell systems (SOFCS) in concert with electric power grids.
Electric power grids typically include a number of power generating systems, such as SOFCS, that supply electricity to the grid and a number of consumers that draw electricity from the grid. When the generation and consumption of electricity are substantially equal, the grid frequency is substantially constant at a particular nominal value. This is the preferred state for optimal efficiency and functionality. The nominal grid frequency is a parameter established by the governing power distribution entity. Examples of nominal standard grid frequencies for the European and North American systems are 50 Hz and 60 Hz respectively.
Transient frequency deviations result from changes in energy consumption and/or the removal or addition of power generation systems. Decreased consumption or increased generation tends to cause an increase in the grid frequency, and vice versa. Power consumption and generation are time-dependent variables which may cause short—i.e., measured in second or minutes—deviations of small magnitude. Larger frequency transients, such as those having a magnitude of greater than 0.3 Hz, may be due to the sudden loss of a significant power generator.
One known way to mitigate the frequency transient magnitude and duration is to have some amount of standby power generation capacity, sometimes referred to as a system reserve. A spinning reserve is an aspect of the system reserve that is derived from already operating generators and is readily deployable. For example, a spinning reserve can be defined as any back-up energy production capacity which can be made available to a transmission system with short notice and can operate continuously for several hours once it is brought online. Frequency generation is often managed by varying the output of fossil fuel-fired generators connected to the electric grid. Not all generators can be effectively operated with constantly varying output, and those that are thus operated incur costs from increased fuel consumption and maintenance. Additional conventional solutions include rapid deployment or removal of load, or added transmission power from other grids. Accordingly, there is a need for both rapidly responsive reserve capacity, and methods and means for utilizing excess power during periods of low consumption by end users.
Solid oxide fuel cells are electrochemical devices that convert chemical energy produced by a reaction directly into electrical energy. Reversible or regenerative cells may also do the reverse, consuming electricity and converting chemicals in a reaction to produce hydrogen gas—i.e., electrolyzing steam. Multiple fuel cells may be assembled together to form an arrangement called a fuel stack. The fuel cell stack may include interconnects/gas separator plates for routing reactants and products through the stack. An example of a fuel cell system is described in U.S. Pat. No. 7,422,810, which is incorporated herein by reference in its entirety. Parameters such as temperature, reactant type and flow rate are determined by a controller, which thereby regulates the type and magnitude of the fuel cell stack output.